A turbulent boundary layer over a two-dimensional rough wall

Djenidi, L.; Antonia, R. A.; Amielh, Muriel; Anselmet, Fabien

doi:10.1007/s00348-007-0372-5

Cited by 58 publications

(43 citation statements)

References 16 publications

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“…In rough open channel flows the non-dimensional equivalent sand roughness, k s + = ku * /ν is greater than 70, and the roughness elements completely penetrate the fully turbulent logarithmic layer. In fully developed open channel flow, the height of the turbulent boundary layer occupies the entire flow depth (d) and thus ≈ d. Recent particle image velocimetry (PIV) and planar light induced fluorescence measurements by Djenidi et al (2008), Manes et al, (2007) and numerical results of Krogstad et al, (2005) document an increase in the Reynolds stresses in the outer layer which was different from that obtained on the smooth wall. Nikora et al (2001) developed a comprehensive classification of rough open channel flows based on the value of the relative submergence (d/k).…”

Section: Rough Open Channel Flowsmentioning

confidence: 99%

Bed Forms and Flow Mechanisms Associated with Dunes

Balachandar¹,

Reddy²

2011

Sediment Transport - Flow and Morphological Processes

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Section: Rough Open Channel Flowsmentioning

confidence: 99%

Bed Forms and Flow Mechanisms Associated with Dunes

Balachandar¹,

Reddy²

2011

Sediment Transport - Flow and Morphological Processes

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“…Thus, there exists many valuable works in the literature that focus on the turbulent boundary layer flow developing on rough walls including coatings. Recent studies of Schultz and Flack (2005, 2007, Afzal (2008), Mejia-Alverez and Christensen (2010), Brzek et al (2010), Cal et al (2009), Djenidi et al (2008) and Bons (2010) are interesting examples of this challenging area of research. Comprehensive reviews of the literature were also given by Jimenez (2004) and Raupach et al (1991).…”

Section: Introductionmentioning

confidence: 97%

Turbulent boundary layer measurements over flat surfaces coated by nanostructured marine antifoulings

Ünal

Atlar

2012

Exp Fluids

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Whilst recent developments of nanotechnology are being exploited by chemists and marine biologists to understand how the completely environmentally friendly foul release coatings can control marine biofouling and how they can be developed further, the understanding of the hydrodynamic performances of these new generation coatings is being overlooked. This paper aims to investigate the relative boundary layer, roughness and drag characteristics of some novel nanostructured coatings, which were developed through a multi-European and multi-disciplined collaborative research project AMBIO (2010), within the framework of turbulent flows over rough surfaces. Zero-pressure-gradient, turbulent boundary layer flow measurements were conducted over flat surfaces coated with several newly developed nanostructured antifouling paints, along with some classic reference surfaces and a state-of-the-art commercial coating, in the Emerson Cavitation Tunnel (ECT) of Newcastle University. A large flat plane test bed that included interchangeable flat test sections was used for the experiments. The boundary layer data were collected with the aid of a two-dimensional DANTEC Laser Doppler Velocimetry (LDV) system. These measurements provided the main hydrodynamic properties of the newly developed nanostructured coatings including local skin friction coefficients, roughness functions and Reynolds stresses. The tests and subsequent analysis indicated the exceptionally good frictional properties of all coatings tested, in particular, the drag benefit of some new nanostructured coatings in the Reynolds number range investigated. The rapidly decreasing roughness function trends of AKZO19 and AKZO20 as the k þ s increases were remarkable along with the dissimilar roughness function character of all tested coatings to the well-known correlation curves warranting further research at higher Reynolds numbers. The wall similarity concept for the Reynolds stresses was only validated for the transitionally rough surfaces from ðy þ eÞ þ % 100 up to the end of the boundary layer.

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“…For a flow of given bulk Reynolds number, R, over two-dimensional roughness elements, the transition between d-and k-type roughness depends solely on the streamwise spacing of the elements. Many researchers have chosen to focus on square bar roughness to investigate the effect of spacing on turbulence structure and mean flow characteristics, both experimentally (Coleman, Nikora, McLean, & Schlicke, 2007;Djenidi, Antonia, Amielh, & Anselmet, 2008;Djenidi, Elavarasan, & Antonia, 1999;Krogstad, Andersson, Bakken, & Ashrafian, 2005;Okamoto, Seo, Nakaso, & Kawai, 1993;Roussinova & Balachandar, 2011) and numerically (Cui, Patel, & Lin, 2003;Ikeda & Durbin, 2007;Stoesser & Nikora, 2008;Stoesser & Rodi, 2004). Simpson (1973), Tani (1987), Jiminez (2004) and Coleman et al (2007) all proposed that the transition from d-to k-type roughness occurs at around l/k = 5, where l is the crest-to-crest bar spacing and k is the roughness height.…”

Section: Introductionmentioning

confidence: 99%

Free surface flow over square bars at intermediate relative submergence

McSherry

Chua

Stoesser

et al. 2018

Journal of Hydraulic Research

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Results from large-eddy simulations and complementary flume experiments of turbulent open channel flows over bed-mounted square bars at intermediate submergence are presented. Scenarios with two bar spacings, corresponding to transitional and k-type roughness, and three flow rates, are investigated. Good agreement is observed between the simulations and the experiments in terms of mean free surface elevations and mean streamwise velocities. Contours of simulated time-averaged streamwise, streamfunction and turbulent kinetic energy are presented and these reveal the effect of the roughness geometry on the water surface response. The analysis of the vertical distribution of the streamwise velocity shows that in the lowest submergence cases no logarithmic layer is present, whereas in the higher submergence cases some evidence of such a layer is observed. For several of the flows moderate to significant water surface deformations are observed, including weak and/or undular hydraulic jumps which affect significantly to the overall streamwise momentum balance. Reynolds shear stress, form-induced stress and form drag are analysed with reference to the momentum balance to assess their contributions to the total hydraulic resistance of these flows. The results show that form-induced stresses are dominant at the water surface and can contribute significantly to the overall drag, but the total resistance in all cases is dominated by form drag due to the presence of the bars.

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A turbulent boundary layer over a two-dimensional rough wall

Cited by 58 publications

References 16 publications

Bed Forms and Flow Mechanisms Associated with Dunes

Bed Forms and Flow Mechanisms Associated with Dunes

Turbulent boundary layer measurements over flat surfaces coated by nanostructured marine antifoulings

Free surface flow over square bars at intermediate relative submergence

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